Selective receiving apparatus for wireless telephone or telegraph sets



Sept. 14, 1937.

SELECTIVE RECEIVING H. P. PRATT 2,093,158

APPARATUS FOR WIRELESS TELEPHONE OR TELEGRAPH SETS Original Filed July 29, 1925 4 Sheets-Sheet l II M3 22 la f/ M ,/06 my m7 72 H. P. PRATT Sept. 14, 1937.

SELECTIVE RECEIVING APPARATUS FOR WIRELESS TELEPHONE OR TELEGRAPH SETS Original Filed July 29, 1925 4 Sheets-Sheet 2 Sept. 14, 1937. P PRATT 2,093,158

SELECTIVE RECEIVING APPARATUS FOR WIRELESS TELEPHONE OR TELEGRAPH SETS Original Filed July 29, 1925 4 Sheets-Sheet 3 Hi9 m 59 I /1 re 1729 Arr y Sept. 14, 1937,. H. P. PRATT 2,093,158

SELECTIVE RECE/LVING APPARATUS FOR WIRELESS TELEPHONE OR TELEGRAPH SETS Original Filed July 29, 1925 4 Sheets-Sheet 4 At y Patented Sept. 14, 1937 UNITED STATES samc'rrvr. RECEIVING srrsas'rus Foa wmamss rsmrnous 0a ransom SETS Harry Preston Pratt, Chicago, 11L, assignor, by mesne assignments, to Harry Preston Pratt, William Frederick Grower, Henry Asa Allen, Howard Thompson Ballard, and George Squires Herrington, trustees Radio Trust acting as Pratt Substitute for abandoned application Serial No. 46,692, July 29, 1925. This application April 20, 1935, Serial No. 17,550

8 Claims. (CL 171-119) This invention relates to selecting tuning apparatus for either wire or wireless telephone or telegraph circuits.

The object of the invention is the provision of a compact and easily adjusted equipment by means of which the receiving equipment may be made responsive only to the oscillations of a definite frequency and emanating from a certain selected sending station.

One of the features of the invention resides in the provision of a plurality of coils or loops of insulated conductor, the loops being mounted one within another and so arranged that the loops may all lie in substantially the same plane or they may be rotated or translated one within the other, so that the planes of the inner loops may be placed at various angles to the planes of the outer loops. The coils may be all connected in series or parallel, or certain coils may be only inductively related to the others depending on the circuit with which the device is used.

Another feature consists in mounting the loud speaker within the center of the innermost coil.

Another feature of the invention resides in the provision of means whereby the rotation of one of the coils will automatically cause a rotation of a second coil relative to the first.

A still further feature resides in additional means whereby the inner coils may be adjusted relative to each other and to the outer coil.

A still further feature resides in the provision of a metal sheet or plate adjacent to the coil which may be adjusted relative thereto in order within the second. The three coils may comprise various numbers of turns and the different arrangements will vary as to the total length of wire included in the coils. While the three coil arrangement shown in the drawings has been found to give very good results, a two coil structure will be found satisfactory for some purposes and for very fine tuning more than three coils may be found desirable.

The coils of thepresent invention may be used to take the place of the usual antenna or they may be placed in series with the usual antenna, or a portion may be connected to the antenna and the remaining portion connected tothe receiving equipment in various ways. By mounting the coils about and within the horn, the receiving equipment may be constructed as a self-contained unit and therefore may be moved from place to place without bothering with antenna connections.

It is believed the invention will be most readily understood from a detailed description thereof, taken in connection with the accompanying drawings, in which Fig. 1, is a side view partly in section of one form of applicant's apparatus comprising three coils nested respectively one within the other;

Fig. 2 is a view of the form of the device shown in Fig. 1, with the inner coils adjusted in relation to the outer coil;

Fig. 3 is another view of the same apparatus but shows each of the coils arranged in a plane at right angles to each of the other two coils;

Fig. 4 is a side view of a modified form of the device in which the conductors forming the several loops are arranged in the same plane instead of side by side as in the device of Fig. 1;

Fig. 5 is a view-of the device such as shown in Figs. 1, 2, and 3 but illustrates the manner of mounting the loud speaker upon and within the innermost coil;

Fig. 6 shows another modified form of the device in which the conductors forming a coil are arranged in zig-zag manner and simplify the required supporting framework;

Fig. '7 is a cross section on the line l'l of the device, shown in Fig. 6;

Fig. 8 is a plan view of the arrangement of Fig. 1, but shows in addition the manner of adjustably mounting the metal sheet or plate in relation thereto;

Fig. 9 is a transverse sectional view through the device such as is shown in Fig. 5, but modified to illustrate a double diaphragm loud speaker within the innermost of the three coils;

Fig. 10 is a section on the line ill-l0 in Fig. 1;

Fig. 11 is a section through the rim of either the outermost or the second coil of the device of Fig. 1, illustrating the manner in which the actuating cord or belt passes over the idler pulleys;

Fig. 12 is a view partly in section of a modified form of the device shown in Fig. 1, whereby the inner coils may be adjusted in relation to the outer coil;

Fig. 13 is another modification of the arrangement shown in Fig. 1, and is adapted to cooperate with the structure shown in Fig. 12 to obtain the result referred to;

Fig. 14 is a schematic diagram of the circuits which have been found to be satisfactory when used with the device of Fig. 1;

' which have been found satisfactory with the form of the device shown in Fig. 4;

Fig. 16 shows a .still further circuit arrangement;

Fig. 1'7 shows a modified form of coil; and Fig. 18 is a perspective view of a modified form. Referring now to the drawings in which like reference characters indicate like parts in the several views, I0 is an annular ring somewhat T shaped in cross section, as shown in Fig. 10. The

ring I0 is supported by and fixed to the column I I which, in turn, is pivotally supported on the rod I2, the lower end of which is fixed to the base I3 in any desired manner. Extending laterally from the column I I and fixed thereto is a handle I4 by means of which the ring or hoop I0 may be rotated about the rod I2 as an axis.

Mounted within the ring I0, and preferably concentrically therewith, is a second ring I5 similar to ring II] but smaller in size, and mounted within the ring I5 is a third ring I6 of similar formation. The ring I5 is provided at one side thereof with the friction collar I'I within which projects the end of the pin I8 rotatably supporting the ring I5. On the opposite end of the pin I3 is a pulley I0 over which passes the cord or belt 20. The cord 20 will preferably make one complete turn about the pulley I9 so as to avoid slipping thereon. Fixed to the upper end of the rod|2 is a pulley or belt wheel 2| about which passes the opposite end of the loop formed by the cord or belt 20. The cord 20 passes over the idler pulleys 22 to prevent frictional engagement of the cord with the ring ID. The idler pulleys 22 are preferably mounted in recesses 23, in the stem 24 of the ring II], as shown in Fig. 10, and strips of veneer or other thin material 25 are preferably secured to the side of the stem 24 in order to provide a finished external appearance. Positioned within the ring III, diametrically opposite the pin I8, is a pi' or pivot member 26. The inner end of the pin 26 is loosely received within the ring I5 and is provided with a pulley or belt wheel 21 fixed thereto,and passing about the pulley 21 is a cord or belt 28 which is similar in structure and function to the belt or cord 20. Mounted within the innermost ring I5 are the pivot pins 29 and 30. Pin 29 is loosely received by the ring I 5. Pin 30 is also loosely received by the ring I 5 but has rigidly fixed thereto the pulley or belt wheel 3| about which passes the cord or belt I8. Idler pulleys 32 are provided for a purpose similar to the idler pulleys 22.

From an inspection of the structure thus far described, it will be noted that when the outmost ring III is rotated by means of handle I4, one lap of the cord 20 tends to wind up on the pulley 2| thus causing the pulley I9 to rotate, which in turn rotates pin I8 and causes the rotation of the second ring I5 relative to ring II). In like manner, as the ring I5 rotates one lap of the cord 28 tends to wind up on the fixed pulley 21 thus causing the pulley 3| to rotate and consequently producing a rotation of the innermost ring l6.

Fig. 2 shows the rings in process of being rotated and Fig. 3 shows the three rings rotated to positions such that each occupies a plane at right tion to each other by moving each separately by the hand of the operator. The pivot pins I8, 26, 29 and 30 are mounted in friction sleeves, such as sleeve IT, to permit this independent adjustment.

Wound about the flange 33 of the outer ring II! (see Fig. 10) is a coil 34 of wire. This coil 34 comprises only they turns shown at the left hand half of Fig. 10. The conductor then passes inwardly adjacent to pivot pin 26 to the middle ring I5 on which it is wound as indicated at 35 in Fig. 3. Again it is to be understood that coil 35 comprises only the turns on the lower half of ring I5, as seen in Fig. 3. After making several turns about ring I5, the conductor passes adjacent to the pivot pin 29 to the innermost ring I6 and is at 31. vThe conductor then passes out adjacent to the pin 3|] and is wound about ring I5 a number of turns, as shown at 38, it being understood, however, that the coil 38 is wound inthe opposite direction to coil 35. Finally the conductor passes adjacent to the pivot pin I1 and is given a number of turns about the circumference of ring III as shown at 39 in Fig. 10. It will be understood that the turns of the coil 39 are in the opposite direction to those of the coil 34. The endsof the conductor will preferably be secured to binding posts on the column II (not shown).

It will thus be seenthat starting from the out-- side, a number of turns are made about the ring I0, then a number about the ring I5 in the same direction, then a number of turns about the ring IS in the same direction. The conductor is then doubled back on itself and similar coils are made on the ring" I6, I5 and I0, all being wound in the opposi direction to the coils first placed thereon.

The structure shown in Fig. 4 may be similar to that of Figs. 1, 2, and 3, except the turns of the wire forming the coils are all in substantially the same plane. The outer frame 43 is carriedby the column 4|. The second frame 42 is pivotally supported from the frame 40 by means ofthe pivot pins 43 and the innermost frame 44 is pivotally supported from frame 42 by means of the pivot pins 45.

Taking the structure as shown in Fig. 4, the conductor is carried first around frame 40 adjacent to the outside slat 46 and thence around and around, each turn being inside the other in series relation. Each of the three coils shown in Fig. 4, is wound in a like manner and the conductor presents a substantially continuous helical like arrangement from the outside to the center, all the turns being in the same direction. The direction of the winding of any coil to the other, however, may be changed by rotating the frame carrying it through degrees. In Fig. 5, the device of Fig. 1 is shown with a supporting member 41 mounted on the ring I6, a loud speaker 48, or other similar device, being carried by the supporting member 41 adjacent to the center of the ring.

The structure shown in Figs. 6 and 7 comprises the three annular rings 50, 5|, and 52 of different diameters, ring 5| being positioned within 50, and 52 within 5|. Coils 53, 54 and 55 carried by the rings 50, 5|, and 52, respectively, are

formed of comparatively straight portions of heavy wire arranged in intersecting relation and are self-supporting except that they are secured to the rings 68, 6|, and 62. i

Fig. 8 shows the device of Figs. 1, 2, and 3 with a metal sheet or screen adjustably mounted adjacent to the coil. The ring l8 has secured to the top thereof, by means of the pin 88, an arm 6|. Slidably mounted on the arm 6| is a sleeve 82 from which is suspended a sheet metal refiector or screen 68. The screen 88 is preferably joined to the sleeve 62 so as to permit rotation to various vertical planes. Due to the pivotal arrangement of the arm 6| and slidably mounted sleeve 62 and the pivotal connection of plate 68 to the sleeve 62, the plate 63 may be moved into various relations to the coils.

Fig. 9 indicates a manner in which double dia-' phragm' push and pull loud speaker may be mounted in the center of the innermost coil.

The diaphragms 64 and 65 are secured to the innermost ring and have mounted therebetween,

' in any .desired manner, the electro-magnets 66 by which the diaphragms are operated. If desired, outwardly fixed flanges 61 and 68 may be provided on opposite sides of the ring IS in the nature of abbreviated horns. It is to be understood that the loud speaker and horn arrangement disclosed will in no way affect the rotation .of the ring l6 within ring I5.

In Figs. 12 and 13 is shown means for separately adjusting the inner coils in relation to the outer and in relation to each other. It is to be understood that the modification shown in Fig. 12 will be positioned at the point occupied by the pivot pin 26 of Fig. 1, and that one of the pulleys in Fig. 12 will be positioned at the point occupied by the pivot pin 28 of Fig. 1, and that one of the pulleys in Fig. 12 will have the same function as pulley 21 in Fig. 1. This figure shows the outer ring Illa, and the next inner ring l5a, which will be the same as above described in connection with Fig. 1, except as to the modification of the operating means. Fixed within the ring |||a is one end of a sleeve III, the opposite end of which is loosely received by the outer flange of the ring l5a. Rotatably mounted within sleeve 10 and the rings Ilia, and |5a, is a sleeve or collar through which extends the adjustable shift pin or plunger 12. The pin 12 is provided with the knob or hand hold 18 by means of which it 'may be moved inwardly or outwardly to the shift operative connections such as will subsequently appear.

Rotatably mounted upon the sleeve II and within the recess 15 in the ring- Ilia, is a pulley or wheel 15. In a similar manner the pulleys 16 and l! are rotatably mounted upon the sleeve within the recess 11 in ring l5a. It may be here explained that the pulley 16 of Fig. 12 has, in certain stages of the device, exactly the same function as pulley 21 of Fig. 1 and will be joined to a pulley carried by the middle ring |5a which will be in all respects similar to the pulley 3| of Fig. 1.

The sleeve H is provided with a pair of slots 18 and 18 and the plunger 12 is provided with a corresponding pair of lugs and 8| adapted to slide in the slots 18' and 19, respectively. The pulleys 15, I6 and 11 have their inner surfaces which are positioned about the sleeve fluted or provided with a series of notches into any one of which lugs 80 or 8|, as the case may be, may be positioned. The right end of the sleeve 10 is also provided with notches or recesses 88 into .consequently pulley 88.

which the lug 8| on the plunger 12 may be positioned.

From an inspection of the drawings, it will be noted that the lug 88 projects into a notch in the pulley l5 and the lug 8| extends beyond pulley 11 into the frame of ring l6a, locking it to the sleeve 1|. Thus it will be seen that when the plunger 12 is pushed into its extreme right hand position, as viewed in Fig. 12, pulley l5 and ring |5a will both be locked to the sleeve II.

If the plunger 12 be moved to the left to its intermediate position, lug 88 will still be in engagement with pulley 15 while lug 8| will have moved into engagement with pulley 11. Therefore in this position, pulleys I5 and 11 will be locked to sleeve 1 I.

It now the plunger 12 is moved to its extreme left hand position, lug 88 passes out of engagement with pulley I6 and lug 8| becomes positioned in a notch 83 of the fixed collar 16, thus locking pulley 16 in fixed position and leaving pulley 15 free to rotate about collar The manner in which these several pulleys function will be described after the structure shown in Fig. 13 has been described.

Referring now to Fig. 13, a base Ila. is shown, to which is secured rod |2a., in the same manner as rod l2 in Fig. 1. Fixed to the rod l2a, as by means of a spline 84, is a pulley 2|a, which has the same function as the pulley 2| in Fig.1. The pulley 2|a. will be joined by a cord or belt 280., to a pulley such as the pulley 2|, Fig. 1. Positioned above the rod |2a, and rotatable within the stand or column lla', is a sleeve 85 to the lower end of which is fixed, in any desired manner, the disc 86 having projecting arm 81 by means of which the sleeve 85 may be rotated. Fixed to the upper end of the sleeve 85, in any desired manner, is a pulley 88. Pulley 88 of Fig. 13 is joined to pulley 15 of Fig. 12 by a cord or belt 89 in the same manner that pulley 8| is joined to pulley 21 by the cord 28 in Fig. 1. Thus when the handle 81 is rotated, sleeve 85 and pulley 86 also rotate and the belt 88 causes pulley 15 to rotate as previously described. However, pulley 15 may be either fixed to sleeve 1| or free to revolve thereon, depending on the position of plunger 12.

The operation of the modification shown in that the plunger 12 is moved to its extreme left hand position, the operation will be substantially identical with that above described in connection with Fig. 1. Thus when the column ||a is rotatedby means of the handle 88, t e cord 28a will wind up on pulley 2|a and caus a rotation of the pulley corresponding to It! in Fig. 1, thus rotating the ring |5a within ring Illa. It will be recalled that when plunger 12 is at its extreme left position, pulley 16 is locked to fixed sleeve HI. Therefore as the ring |5a rotates, the cord or belt 9| will wind up on pulley l6 and, acting on a pulley such as 3| ofFig. 1, will cause the innermost ring to ,be rotated. The rotary operation of the coils thus far described may be for the purpose of tuning in roughly the desired station or other like purpose.

When it is desired to adjust the inner coils relatively to the outer one independently of the means which causes the coils to rotate in unison, handle 81 is operated to rotate sleeve 85 and Assuming that the plunger 12 is in its middle position, pulley 11 will now be locked to sleeve 1|, thus, as the pulley 88 rotates, the movement thereof will be transtimed through cord as to pulley I which will act to rotate the sleeve 'II and consequently pulley ,II. 'Pulley II will be joined by a cord or belt to a pulley carried'by the upper end of a pivot pin such as 29, of Fig. 1. shift plunger I2 is in intermediate position, the rotation of collar 05 will efiect the movement of the innermost coil relative to the other two.

When the plunger I2 is moved to its innermost position, pulley I5 and the ring I5a will be locked to the sleeve II. Thus, if the sleeve 85 be. now rotated, the niiddle coil will rotate within the outer coil I0a.

Referring now to Fig. 14, an attempt has been made, to show the three coils, each divided into two parts wound in opposite directions. Starting from the conductor 95 which is joined to the antenna, the wire is wound in a counter-clockwise direction about the outermost ring, then passes inwardly as indicated at 96 to the middle ringabout which it is wound in the same direc- ,tion and 'thence'it passes inwardly as indicated at 91 to the innermost ring about which it is wound in the same direction. The wire is now doubled back as indicated at 98 and is wound about each of the three rings in a similar manner but in the opposite direction. The terminal of the wire 99 is associated with the receiver in any of the many well known manners. The device has been found to give very satisfactory results with the point I8 connected to ground. Good results have also been obtained when no ground connection was supplied to 98. As a matter of fact, the tuning arrangement just described has been found to give very satisfactory results when connected into the receiving circuits in many different manners.

In Fig. 15, the three coils of the device are shown connected in series, one end of the conductor being joined to the antenna I00 and the other end IOI being joined to the receiver.

In Fig. 16, a still further circuit arrangement is described. In this arrangement one coil I02 has one of its ends joined to the antenna I03, the other end I04 being open. Another coil I05 has its end I06 grounded, the opposite end I0I being open. The third coil I08 has its opposite ends joined to the coil I09 which is inductively associated with the receiver. Under certain circumstances, the open ends of coils I02 and I05 may .be joined together advantageously.

In Fig. 17, there is shown a conductor I I0 comprising insulated wire wound in spiral formation about a flexible member III. The flexible member I I I may be either a cord or of conducting material, as a wire. The conductor thus formed may be wound about the rings heretofore described to form a coil of spirally arranged wire, as indicated at I I2. Where the wire is employed for the flexible member III, the member III may under certain circumstances be used as the secondary, the wire spirally arranged thereabout, acting as the primary.

It has been found that when a structure employing a plurality of coils of wire, such as herein disclosed, is rotated, it acts to change the frequency of the circuit and thus stations may be tuned in and tuned out by rotating the coil structure as a unit without rotating them in relation to each other. For instance, if a structure such as found in Fig. 1, but having the driving pulley arrangement omitted, is rotated, the sending sta- Thus when the tatlng the coils as Just described, itis ouite likely that other stations will also be audible. If now the several coils are adjusted in relation to each other, a point of adjustment will be found wherein all except the desired station will be tuned out.

Thus the device herein disclosed may be employed several circuit diagrams, one of the coils has been described as connected to the antenna, the arrangement has been found to give very satisfactory results where no antenna is employed, it being used both as an antenna and as a tuning device.

It will be noted that as the coils are rotated they not only change their inductive relation to each other, but also change the relation of the planes of the coils to the point from which the electrical oscillations emanate. It is thought that this feature of changing the relation of the plane of the coil to the direction from which the oscillation originates has a material efiect on the tuning operation. Furthermore, if one of the inner coils is rotated through an angle of 180 degrees, its relation to the other coils is reversed. There are a large number of ways in which the coils herein disclosed may be adjusted in relation to each other and connected to a receiving circult.

Referring now to Fig. 8, the operation of the shield or screen 63 will be described. It has been found that after the coils have been rotated so as to bring in the desired sending station, a very material tuning effect will be produced by adjusting the relation of a metal plate, such as shown on 63, to the coils. This plate 63 may be grounded or merely suspended in insulated relation. The plate 63 perhaps affects the capacity of the circuits and it is thought it likewise may have a shield eiTect. The experiments with the plate 63 have not been carried to the point where the theory of its effect is clearly understood. However, it has been absolutely determined that it does have a very material tuning efiect. In many cases the shield acts not only to eliminate the undesired station, but seems to cause amplification of the oscillations received from the desired Station. The shield may be used when rotating the coils as a unit to bring in the desired station and also to effect a tuning operation when the coils have been rotated in relation to each other.

It will be noted that the arrangement of Fig. 5 shows the column II joined to the base through the medium of a pivot joint H5 which may be held in locked position by means of a butterfly nut II6. This permits the coils to be tilted as well as rotated.

One method of rotating the coils is shown in the drawings but many other ways may be readily designed. For instance, a small flexible shaft and crown gears may be substituted for the pulley and cord arrangement. Also by properly arranging the pulleys and anti-friction rollers, a single continuous cord or belt may be employed.

The coils may be used in many different circuit arrangements. The coils may be arranged in series, parallel or series parallel and either electrically or inductively related. Also for certain tuning operations it may be found desirable to take off taps from certain points of the coils which may be carried to a circuit controlling device separate from the coil structure.

Instead of providing a small fiat base, as shown in the drawings, a base having a cavity or recess therein may be provided, the recess being employed to receive the tubes and other parts of the equipment.

The coils shown herein may readily be employed to take the place of the present antenna coils.

Fig. 18 is a perspective view of a modified form of the apparatus, in which the wires of the coils are supported by two separated annular members Ill connected by cross members H8 and having tubular axial members I 19 containing wires leading to the various coils. A switchboard I20 is mounted on the base and provided with sockets Ill and plugs I22 carried by wires I23. The sockets l2! have their wires connected to different parts or sections of the outer coil. By this arrangement connection may be made to the outer coil, so that either the whole or any part of this coil may be connected in circuit.

While in the drawings and in the above specification, certain forms of the invention have been specifically disclosed, it is to be understood that many other modifications of the de ice are contemplated by the inventor and the invention should therefore be limited only by the scope of the appended claims.

This application is a substitute for application Serial Number 46,692, filed July 29, 1925 (renewed March 25, 1933), Selective receiving apparatus for wireless telephone or telegraph set.

Having thus described my invention, what is claimed as new and is desired to be secured by Letters Patent of the United States is:-

1. In radio apparatus, a base, a coil and means for rotatably mounting said coil on said base, a second coil within said first mentioned coil, means carried by said first coil for supporting said second coil in pivotal relation thereto, a third coil within the second coil and means on said second coil for pivotally supporting said third coil, and means interconnecting said coils whereby they may be rotated in unison each in relation to the other.

2. In radio apparatus, a coil and means for pivotally supporting the same, a second coil within said first mentioned coil, each of said coils comprising two parts wound in opposite directions, and means carried by said first mentioned coil for supporting said second coil in pivotal relation thereto.

3. In radio apparatus, a coil and means for pivotally supporting the same, a second coil within said first mentioned coil for supporting said second coil in pivotal relation thereto, and a third coil within the second coil and means for pivotally mounting said third coil on said second coil, each of said coils comprising two parts wound in opposite directions.

4. In a radio apparatus, a supporting base, a coil supported by said base, an inner coil supported by said first mentioned coil, shaft and pulley means located in said base and said coils, for rotating said coils in relation to each other and to said base.

5. In a radio apparatus, a supporting base, a coil directly supported by said base, a coil supported by said first mentioned coil, means in said base and said coils for rotating said coils in relation to each other, control means in said base for operating said first mentioned means, said coils having interlocking means for holding them stationary with respect to each other when said control means is applied.

6. In a radio apparatus, a base, a coil pivoted on said base, a second coil pivotally mounted on said first coil, a third coil pivotally mounted on said second coil, and operating means mounted on said base for bringing about turning movement of all of said coils.

'7. In a radio apparatus, a base, a coil pivoted on said base, a second coil pivotally mounted on said first coil, a third coil pivotally mounted on said second coil, and operating means mounted on said base for bringing about relative movement between said coils.

8. In a radio apparatus, a base, a coil pivotally mounted on said base for turning movement in one plane, a second coil pivoted on said first coil for turning movement in a plane at right angles to the plane of the first coil, a third coil pivoted on said second coil for rotation in a plane at right" angles to the plane of rotation of said other coils and operating means mounted on said base for bringing about turning movement of each of the coils relative to the other in their respective planes of rotation.

HARRYPRESTON PRATT. 

